The active control devices for vehicles currently known to be in development, especially for aircraft, also called active side-sticks, do have over the conventional inceptors the advantage that artificial corresponding control forces can be applied by actuators to the control input device so that the driver of the vehicle gets a real control-feeling. Therefore, the operator or driver has the feeling that the control input device actually represents mechanical elements, such as springs, masses, buffers or friction brakes, and is mechanically connected to the control elements of the vehicle, such as elevator assembly or rudder.
Such active inceptors can also be utilized to transmit to the operator or driver tactile information so as to provide an additional information channel. Such tactile information could be represented differently, for example by vibration for non-directional information or local force variations for directional information. A local force variation in the form of a so-called soft stop does have—for instance—the effect that the spring force gradient increases markedly from a certain position on so that the operator or vehicle driver can be informed in a haptic way about the reaching of any limit which is dependent on the path of the control. Such indications are also called “tactile cues”. The decision to follow such a “tactile cue” or to bypass it is up to the operator or driver.
A big problem with this type of information transmission constitutes the fact that the operator or driver must be in contact with the control-input-device so that information transmission can take place on this information channel and so that the tactile indication which is placed on the control-input-device can be perceived by the driver. If the vehicle—for instance—is controlled using a manual control input device (sidestick, joystick) the driver must clasp the control input device with his hand in order to be able to perceive the information. Would he let go, the control surface would follow the force gradient of the “tactile cues”, unnoticed by the driver/operator which in turn means that the vehicle would follow the applied control movement. It should be noted that the force applied to the inceptor should not represent any real control movement of the vehicle, but merely serve to provide to the driver/operator a piece of information. That the vehicle has carried out a control movement due to the “tactile cues” would be noticed by the driver only if the motion deviation would be greater than his perception threshold which can lead to dangerous situations.
It is therefore very important that with this type of control input device that information for the driver/operator is applied to the inceptor only after the control input device has detected for certain that the driver/operator is in contact with the control input device of the vehicle, i.e. is clasping it with his hand.
Another application which makes detecting a contact state necessary is to stabilize the control input device itself. The control input device is subject to accelerations which are caused by gravitational acceleration, the movement of the aircraft or vibration. The control sensors of the control input device can not differentiate these inertia forces from the desired forces of the driver/operator which can lead to unintended control inputs. Control contact detection can be used within the control surface so fact it can only be adjusted if a hand is placed on it or is grasping it.
From DE 10 2007 039 332 A1 a method and steering assistance for the detection of a contact state is known to detect if at least one hand of a driver is grasping the steering handle of a vehicle. In this method a contact state of the hand on the steering wheel is detected by comparing the measured sensor data for a moment sensor and an angular sensor with a model of a free steering movement which is done via a so-called state observers. The state observer estimates if the driver's steering torque moments and determines whether the hands are on the steering handle. The disadvantage is that an accurate modeling of the steering mechanics is required, and ultimately the state observer can only give an estimate and such estimate is not enough for reliable detection if a hand is grasping a control device during flight operations.
Furthermore, DE 10 2008 021 150 A1 discloses a method in which a lack of driver activity is determined over a period of time, i.e. indirect detection of the probability of a contact can be determined in regards to the steering handle. For this purpose the steering activity is determined over a certain period of time and stored, thus it can be determined if, over a period, steering activities have taken place. Over a threshold value it can then be determined based on inactivity over a time period if there has been any inactivity due to lack of contact. This method also has the disadvantage that it can not precisely determine whether a contact between the driver/operator and control input device does actually exist. Additionally, this method can not determine whether it is an intentional, unintentional or manual control device angle change which was caused by acceleration, as only the driver activity is checked.
Another method which relates to the analysis of driver activities, from DE 103 58 494 A1, is known, where the driver's actual behavior in a given situation is compared with a predetermined reference handling. If it is detected that the actual behavior of the driver deviates much from the reference behavior stored in a database, in this given situation, for example, at very high speed, then the driver assistance system is activated and takes over to prevent serious accidents. Again, only lack of driver activity can be concluded, but not whether there is actually a physical contact between the control input device and driver/operator.
The methods known of current state of the art all have presently the disadvantage for the task at hand that they can not ascertain with sufficient accuracy if actual physical contact between the control input device and driver/operator does exist, however, this is especially needed during flight operation. Without such a sufficient accurate “hands-on” detection active control input devices in aircrafts can not be operated safely.